Better Halves
by bravevulnerability
Summary: 'They're all in pairings, cut into halves, and if this is a study into separation anxiety, then it's definitely working. Even though Castle technically isn't her other half.' An AU version of 8x12, 'The Blame Game', set in season 3.


_Can you meet me? It's urgent._

Kate pierces her bottom lip between her teeth as the message flashes across the screen of her phone, types back her response, and begins to rise from the couch.

 _Address?_

"Hey, where're you going?" Josh questions, his eyes dropping down to the phone in her hand. "You said you had the night off."

"I do," Kate murmurs, diverting her eyes from the accusation that comes alive in his.

"Then where are you going?" he continues, his tone of voice patronizing, like one he would use on a child who's just been caught doing something wrong.

The last thing she needs is another lecture.

"It's him, isn't it?" Josh comes to his own conclusion, shooting up from the couch to follow her towards the coat closet, slamming the lid of her laptop closed on the movie they had settled in to watch as he goes. "The _writer_?"

She purses her lips at the sneer of Castle's title in Josh's mouth and shrugs into her jacket.

Since the freezer, since nearly succumbing to the cold and dying in each other's arms, she had attempted to be there for her partner, to be the person who understood, who talked him through the nightmares where they didn't make it, where the bitter cold had conquered. And in turn, Rick – _Castle_ , she chastises herself, not Rick – had done the same, always answering on the first ring no matter how late, or early, she tended to call him, breathless and certain he'd remained encrusted in the ice.

"We're both okay, Kate," he would always promise her, so soothing and warm, her first name a rich husk slipping past his lips like a secret in the darkness of night. "Do you want to come over? I have hot chocolate."

She wants to say yes. Every time.

"Thanks, Castle. But I'm fine."

"Kate, this is supposed to be our date night," Josh huffs from behind her, pulling on his own coat, she notices. Because she isn't comfortable leaving him alone at her place, not after he had stumbled across her homemade murder board still tucked away behind window shutters and approached her about it as if her mental health had been compromised.

"Your shift starts in an hour," she reminds him, as if it makes the fact that she's practically running out the door to meet with her partner, running out on her boyfriend for another man in the middle of 'date night', any less wrong. "Castle just had a theory on the case and-"

"And you can't tell him no, can you?" Josh mutters, brushing past her for the door. "Ever since the damn freezer-"

"Are you sure you want to finish that sentence?" she snaps in reply. Josh doesn't know trauma. He knows how to witness it, how to sort through the aftermath of it, how to put a band-aid on it and consider it fixed, but he has no idea how to endure it, to deal with it.

Not like she and Castle did.

"Honestly, no. We've already had this argument."

"Well, let's not repeat it," Kate mumbles, tugging the door shut behind her and locking up.

"Call me if you ever get a chance. We need to have an actual talk about this relationship, both ours and the role he plays in it."

Kate rolls her eyes when Josh turns his back to her, already striding for the elevator with his shoulders at his ears. Her boyfriend had turned down a trip to Haiti for her, had put her above his true passion in levels of importance, and she had thought that was what she wanted. She had thought it meant they had a chance.

But as her phone buzzes with another message from Castle and relief threads through her veins, the thought of seeing him soothing the simmering irritation filtering through her bloodstream, she wonders if she had been kidding herself all along.

Kate memorizes the address and takes the stairs to the ground floor to ensure she misses Josh on her way out.

 _143 Nicholas St._

* * *

Castle's heart sinks when he sees Kate on the tiny television screen, horror churning in his guts as this sick game becomes even worse. The kindergarten classroom holding the women is identical to the one he and the three other men are trapped inside of and it doesn't look like they're any closer to figuring out a solution than their significant others are. Well, two of the men's significant other's and his… his Beckett.

They were partners, it still made sense that they were considered a pair in this twisted turn of events, right?

And Kate is smart, smart enough to work through the puzzles and avoid the traps, unless her teammates weigh her down. Like his are beginning to. Whoever is behind this psychological thriller wants them all to turn on each other and it's working.

"So, who is she to you?" the minister, Todd, asks him, still recovering from his lethal combination of encountering a bee and receiving an injection of poison, while Judah and Simon bicker over the latest clue, one trying to break down the door, the other cursing under his breath. "I mean, not to pry, but aside from me, the other guys here both have a wife and a girlfriend…"

Castle rubs at the back of his neck, but the knots that have formed along his nape aren't going anywhere anytime soon. "We uh, we work together. She's my partner."

Todd gives a slow nod, a little disbelieving, but he doesn't have to explain himself, or his lack of relationship with Beckett. It's not as if it matters anyway, not if they don't make it out of here alive.

"Would you be willing to die for her?"

Rick whips his head towards the minister who stares back at him with curiosity, some concern behind the gleam of his glasses, before he raises his hands in supplication. "I'm only asking because it seems to be this guy's theme. One or the other."

"I've always been willing to do that," Castle answers reluctantly, sifting through a row of cubbies for the elusive key they're looking for, wary of every object he touches.

"Yet you aren't a couple. Interesting."

Rick ignores him this time, his eyes landing on the beheaded axe left on the desk, the shape familiar.

He would go to any means necessary to protect Kate Beckett, he thinks he's proven that, but he doesn't intend for anything of such drastic caliber to occur today. They're getting out of here, Kate's group will too, and maybe – just maybe – this will be the life or death scenario that gives him the nerve to just come right out and say the words she never finished a week ago in the freezer.

* * *

Her eyes hungrily drink in the sight of Castle each time he appears on the television screen, eagerly searching his body for any form of injury each time, but it isn't Castle who has apparently become a victim of their captor's game.

"Simon," Meadow whispers, her gaze on her husband's dead body, a crimson stain spreading across the front of his sweater vest, and the gun in Castle's hand.

"I'm - I'm so sorry," Kate gets out, but she doesn't believe that Castle killed the other man, not for a second. It's another manipulation by their kidnapper, just another-

"Save it, your boyfriend killed him."

"He's not my-"

"I don't care what he is or isn't," Meadow cries, blinking back tears and dropping her head, allowing her hair to fall in a curtain around her face. "Your partner killed mine. Just - just get away from me."

Kate steps away from the woman slumped in the chair with her creative brand of handcuffs and rubs her fingers over the temporary tattoo below her collarbone, wondering if Castle is marked with one as well, but from what they've gathered so far, she has a feeling his skin is bare. Meadow doesn't have the symbol, but Patricia does, and it leads her to believe that Meadow's dead husband is tagged with the tattoo as well.

They're all in pairings, cut into halves, and if Patricia is right, if this is a study into separation anxiety, then it's definitely working. Even though Castle technically isn't her other half.

Why hadn't their captor chosen Josh, her actual boyfriend, for this couples version of a sadistic escape game?

"So, not your boyfriend?" Patricia asks minutes later, while they're scavenging for supplies to build their makeshift explosive, the fear in her eyes momentarily overshadowed by intrigue. "The man in the other room, Castle?"

"No," Beckett sighs, plucking a tube of Play-Doh from a shelf and handing it to the other woman. "Just friends."

"You don't look at him like just a friend when he shows up on the screen," Patricia remarks with a small smile, not quite as teasing as Lanie, but close enough to evoke an eye roll.

"Why does it matter?" Beckett huffs, carrying their findings back to the desks they've pushed together for a workstation.

"I'm sure as a homicide detective, you face stuff like this pretty often," Patricia assumes, but Kate shakes her head and scrapes a hand through her hair.

"No, we've actually never faced anything quite like this."

"My point is that I know the minute I'm out of here, every second with Judah will be twice as precious to me. Just suggesting that maybe you embrace that mindset with your… with Castle."

Kate swallows, but focuses her attention on recalling the steps for constructing a small bomb.

"You love him?'

"Patricia," she grumbles, and the other woman grins sheepishly.

"Sorry, talking about anything other than the situation we're currently trapped in helps keep my mind from going into a panic," she explains, ripping into the bright yellow Play-Doh.

"I'm glad you found a helpful distraction amidst all of this, but I'm not answering that question."

The smile curls at the corners of Patricia's lips. "That's answer enough."

* * *

The muffled boom of an explosion sends his heart ricocheting through his chest, crashing into his ribs, and he works harder with Judah to wedge the metal legs of a school desk between the lock and the frame of the door, just inches shy of prying it open.

"What was that?"

"I don't know, but we need to get out of here. Now," Castle murmurs, using all of his strength to widen the wedge between the lock and the frame, every muscle in his arms straining until the steel finally pops open and Todd rams his shoulder into the door.

The three of them spill out into the empty hallway, the walls grey, the pale blue glow of fluorescent lights eerie, and the faint scent of smoke in the air.

"It sounded like an explosion," Todd whispers from the back of their group, and Castle automatically quickens his step, fighting the urge to race down the hall, search every possible room until he finds Beckett.

"Hey man, slow down," Judah hisses from behind him, but all he can think about now is Kate and explosions and how the two are already too intimately acquainted for his liking.

They're just about to turn another corner, Castle stepping around the edge of the wall first, only to be met with the barrel of a gun between his eyes.

"Whoa, whoa, don't shoot," he gets out, the gun immediately lowering to reveal Kate's wide eyes staring back at him. "It's rigged to kill the shooter. That's how Simon died."

Beckett empties the gun of its bullets, drops the useless weapon to the concrete flooring, and surges into him with her arms already snaking around his neck.

"Thank god you're okay," she breathes, her fingers digging into his back and her cheek pressed flush to his. It reminds him of the celebratory hug they had shared last week, after he had yanked the wires from the bomb, saved the city and received Kate Beckett's arms around his neck, the scent of cherries in his nose and her laughter in his ear, as reward.

Castle returns her embrace, buries his nose in her hair and resists the sudden and ridiculous temptation to lift her off the ground and spin her around in the cramped hallway. They weren't free yet.

"Are you okay?" he murmurs, splaying his palms beneath her shoulder blades, able to feel the slight tremble through her bones even as she nods.

"Yeah, yeah I'm fine."

"We should keep moving," Todd calls from over Castle's shoulder.

"He's right." Castle turns to follow the other man, but Beckett grabs his hand, her fingers curling around his while their palms meet in a firm kiss. He looks to her in concern, but she meets his gaze without a flicker of hesitancy in hers.

"I just don't want to get separated again."

Rick flexes his fingers, rearranges the fit of their hands so he can lace his digits through hers.

"We won't," he promises with a soft smile, starting down the hall with the rest of the group, sticking close to the wall with Kate at his side.

* * *

Their only exit slams shut the second the man with the glasses, Todd, rushes for it, and the entry to the hallway at their backs does the same. Stuck within the confines of their captor's endgame, the red numbers of the large timer attached to the wall counting down from five minutes, Kate is the one to find the note dangling from the camera amidst the others' panic, bile rising in her throat with every word she reads aloud for the rest of the group to hear.

"Of those who remain, only your better half can survive."

"What the hell does that mean?" Judah demands.

"There are six of us left and three levers, he wants to separate the couples. Make us choose who goes free," she concludes, her gaze already falling to the lever she intends to pick if her theory is in fact correct.

Castle can't stay, she won't let him, and besides, he is the half that deserves to live on if one of them has to die in the next five minutes. He's drawn out the good in her over the last three years, the brighter parts she had thought were forever dimmed, overshadowed by grief. He had made her better and the least she could do in return was allow him a chance to escape knowing his life had been the best part of hers.

It's the minister who tests her theory, preaching about faith before pulling the first lever, all six of them breathing a sigh of relief when the place doesn't burst into flames. One explosion in one day was enough for her.

"We're running out of time," Todd reminds them with a little too much urgency, his grip on the lever tightening. "You need to choose which ones of you are staying here with me."

Patricia wraps her arms around her boyfriend, Meadow glances to the door with trembling lips, and Kate turns to Castle, but the resolve is already rippling through his eyes, spreading across his face and – oh no.

"I'll stay."

" _No-_ "

Castle's hand covers the lever, tugs it down before she can stop him, her chest clenching as her stomach drops out, and her feet are carrying her to him before she can stop that either.

"What the hell are you doing?" she demands, her heart in her throat, causing her eyes to sting with the threat of tears she refuses to acknowledge. "You can't stay, Castle. Switch places with me-"

"No," he argues, his voice calm, soft but fierce, leaving no room for her protests. "I – they said our better half gets to live. You're mine. So you're going."

"You can't do this," Beckett repeats through gritted teeth, finally indulging in the urge to reach for him, curling her fingers around the collar of his shirt, the edge of her thumbnail glancing off the warm skin of his throat. "What about Alexis and your mom? I won't be responsible for Alexis losing her father and Martha her son."

Castle's free hand lifts to settle along her waist, the span of his palm draping her hipbone in heat, and her body cants forward without her consent. "You're not responsible. This is my choice, Kate."

"Choosing to die?"

"Choosing you," he corrects, his throat bobbing with a rough swallow, and Kate trails her hand higher, traveling the column of his neck to fit her palm to the bone of his jaw, her fingers grazing his ear, the sensitive skin beneath.

"Why?" she whispers, chokes, one of the obstinate tears slipping free, cascading down her cheek. She already knows his answer.

"I love you, Kate."

They're already so close, his chest an exhale away from hers, she only has to lean in to catch his lips in a kiss, her palms at his nape and her fingers tangling in the fine hairs at the base of his skull. Castle's arm automatically cinches around her waist, cradling her body through its rise into his, and for one glorious moment, there is only this – the flawless fit of his lips, soft and pliant against hers, opening at the gentle sweep of her tongue to the seam of his mouth, his taste flooding her with memories of another kiss from mere weeks ago. One she had dreamed about more often than not. But this is better; this one is real. The reassuring weight of his arm, the heat of his body, the thud of his heartbeat pounding in tune with hers, in sync - always so in sync – and Castle sighing his surrender against her mouth.

But as quickly as that moment of bliss comes, it's forced to go, giving way to the urgency at their backs, the glaring red of the timer counting down, the anxious eyes of Meadow, Patricia, and Judah awaiting their decision, attempting to decide the next sacrifice.

"I'm sorry, Castle," she breathes, dusting one final, lingering kiss to his mouth and allowing her fingers to trickle down his cheeks, her palm landing over his chest before she feels his arm fall away from her, encouraging her to take a step back.

Kate keeps her eyes on him, the merciful smile of understanding on his lips, as she drifts across the room, watching it fall apart when she jerks the other lever down.

* * *

"Beckett," he growls, his heart still racing, his lips still tingling from the press of hers, but the doors are already sliding open.

"The instructions said your better half, you're breaking the rules!" Todd protests, his face blooming red with what looks like fear, but Rick senses waves of aggravation radiating from the man instead.

"Screw the rules," Kate snaps, her knuckles shining white around the black lever, her eyes sweeping back to snag his. "I'm staying."

"There's gonna be consequences for all of us!"

"There's consequences when you follow the rules too," Judah states, panic in his voice as he looks to his girlfriend, as if he fears Beckett might change her mind.

But Kate remains resolute where she stands, nodding towards the freedom that awaits the others, watching it disappear once the three of them have scrambled outside and the Todd abandons his post, the gleaming metal door sealing them in once more.

"We know it's you," Castle tells Todd, watching the other man turn on the spot, features already twisting into scowl. He curses under his breath before retrieving a remote from his pocket, clicking a button that has a panel in the wall opening to reveal a waiting shotgun.

Kate inserts herself between them, the barrel of the gun pointed at her chest and a warning in the air before Todd asks what gave him away, demands their explanation and shakes his head in disappointment as they both point out the flaws in his planning.

"One of you has to die, those are the rules," Todd states, his lips in a firm line of frustration, his finger hovering above the trigger.

"Why are you doing this?" Kate inquires, receiving a flood of information, managing to coax a confession from a killer without even trying while Castle steadily drifts backwards, an idea sparking in his head as his eyes land on the levers again.

"One of you has to feel what I felt," Todd continues, his attention fixated on Beckett, his anger, and Castle throws in a few remarks in her defense, helps keep Todd talking, all while silently screwing loose the nearest lever from its post. "When one of you goes free, and tells how I killed your one true love and myself, only then will the world truly understand the monster my parents created. Now, no more talking. Time to solve the final puzzle. Which one of you dies?"

Kate squares her jaw. "I won't choose."

"Neither will I." Especially not after this guy had openly referred to Beckett as the love of Castle's life and she hadn't even blinked.

"Decide, or I'll start maiming you 'til someone does," Todd snaps, aiming his gun at Beckett's foot and Castle speaks up, his heartbeat so loud in his ears, so harsh it feels as if it shakes his entire body from head to toe with every strike to his ribs.

"Okay, okay, I'll choose," Rick promises, earning a horrified flicker of Kate's eyes towards him, but they've always been good at speaking without words, and she must read the reassurance in his gaze, the _don't worry I have a plan_ he attempts to convey with a single lock of their eyes. "I'll decide."

"Good, who dies, Rick?"

Castle tightens his grip on the lever.

"No one dies." He swings, makes contact with Todd's jaw while Beckett lunges for the gun, aims the shot Todd fires towards the ceiling before jerking it from his grasp and redirecting the gun onto him.

In the next moment, the door slides open, Ryan and Esposito are swarming the room, flanking Beckett on either side with their guns positioned on Todd, and Castle watches her chest finally expand with a deep breath.

"You guys okay?" Esposito asks, hauling Todd up from the floor, handing him off to the fellow officers crowding the doorway.

"Yeah, thanks for rescuing us," Kate chuckles, but her eyes are on him, her smile too, and there's so much he needs to say, preferably once they're out of the game room from hell. "Castle, you coming?"

He blinks, stumbles after Kate and the boys already heading out into the daylight, but stops short at the offering of her hand extended towards him.

"Is that offer for hot chocolate still open?"

Castle takes her hand, raises her knuckles to his lips while the boys have their backs turned. He isn't sure of her status with Josh, of what they are now, if their kiss, his confession of love for her, during what could have been their final moments will be another thing swept under the rug, never to be spoken of again. But her eyes are shimmering green, the flecks of gold alive and dancing like firelight, hopeful, beautiful, and not at all what he had been expecting.

It has him believing that she'll only continue to surprise him.

"Always."


End file.
